There is today a need of producing rotor blades of a material, which may resist an aggressive environment, for instance, in the chemical process industry, and which are relatively light, resulting in that the fan, on which the rotor blades are mounted, may be operated at higher speed and that in certain cases, the rotor blades may also be made smaller and thus less expensive. Attempts have therefore been made to produce rotor blades of composite material, such as fibre reinforced plastic.
Through U.S. Pat. No. 4,877,376 a rotor blade of fibre reinforced plastic is previously known, which has relatively low weight and may accordingly be operated at high speed. However, the fastening of the rotor blade is complicated, partly due to a bolt joint having bolts extending through a pressure flange, abutting against the plastic material, to a hub or an attachment device, and partly due to a shank, which extends into the attachment device and co-operates with means to provide a pre-stress of the rotor blade. In an aggressive environment such fastening is unsatisfactory, even if the material in the rotor blade is chemically resistant, the area around the pressure flange will be both chemically and mechanically affected. Thus, it has been shown that rotor blades, having fastening means of this kind, are subjected to great stress, during high speed, and thus tend to be destroyed by propagating cracks, arising in the area of the bolt joint.
Through U.S. Pat. No. 4,966,527 a rotor blade of fibre reinforced plastic is also previously known, which has relatively low weight and may accordingly be operated at high speed. However, the fastening of the rotor blade is complicated, with fibres forming loops around several mounting elements near the blade root, which elements extend substantially parallel to the sides of the blade.